Larissa
Larissa is the largest of the inner moons of Neptune. Its diameter is estimated to be 195 km. It orbits at 73500 km from Neptune and takes 0.555 Earth days to complete one rotation. Physical characteristics Larissa was imaged to have a nearly spherical shape. Details of its surface are not clearly resolved on images token by Voyager 2. It is supposed that image details are craters. Larissa has a very low albedo (0.09). It appears grey in color, which means it does not have significant deposits of tholins on its surface. Estimated density is 1.2 kg/l. At this low density, it must be made of water ice, with impurities, some sort of dirty ice. It is supposed that when Neptune captured Triton, its gravity broke apart the former moons. Some fragments escaped into solar orbit, some fragments collided on Triton and the remaining fragments merged to form the inner moons. If so, Larissa must be a pile of rubble, made by fragments kept together by a weak gravity. Because Larisa lies close to Neptune's Roche limit, it has a very small Hill sphere. Therefore, there are no safe orbits around the moon. Because Larisa lies below Neptune's synchronous orbit, it slowly spirals towards the planet, risking to be broken apart into a ring once it gets closer. Possible interior structure If Larissa is a pile of rubble, then we can expect it to have a very porous structure. Given its small density and high expected porosity, we can speculate that the moon contains a significant amount of heavier elements. This is confirmed by its low albedo. Since Larissa is expected to be newly created from fragments, we can expect that thermal energy from radioactive decay did not heat its core up to water melting temperature. The moon might still contain its initial fragments, only gently compressed by its weak gravity. All these aspects account for a special kind of distribution of minerals and ices. Fragments that came from the icy crusts of former moons will have a high concentration of ice, while fragments that came from former solid cores will have a high concentration of rocks. There is a high chance that fragments are still there, on the moon, undifferentiated. So, there must be an incredible diversity of rocks. Economic importance Larissa is too small for terraforming. It still can have a significant economic importance. The presence of many fragments, of different origin, means that Larissa will be a good destination for mining. Many, if not all celestial bodies that orbit beyond Jupiter, have high concentrations of water ice, usually in the form of a thick crust, blocking access to their cores. On Larissa, miners will find important resources close to the surface or deeper. Because of the low gravity, mining will be more easy then in case of a larger celestial body. Even more, we suspect high porosity, which means that there can be many natural caverns beneath the surface. These caverns can be used as passages to deeper mineral deposits. With many important minerals around, Larissa might even develop other industries, becoming an industrialized moon. All this suggests that Larissa is a good candidate for Industrial colonization. Larissa colony If the moon has many caverns, they can be used for future colonies. They need to be well insulated, to protect the colony from the chill cold outside. Also, heat from interior can melt the walls of ice, if a good insulation is not used. Because Neptune is too far away from the Sun, solar panels are out of question. The colony will have to use a nuclear generator. A fusion generator can use existing hydrogen or deuterium from ice. A fission generator might be possible if enough uranium ores are discovered. Plants can hardly survive at the luminosity found around Neptune (see Plants on new worlds for details). However, growing plants on the surface of Larissa will require huge greenhouses, well insulated or well heated. It will be better to grow plants inside the moon, heated and illuminated with the help of a nuclear generator. On the surface, there will be built a base. Ships landing on Larissa need to be anchored, so that they will not escape into space. Because of the low gravity, which is 3300 times weaker then Earth's, even an astronaut, trying to jump on the surface of Larissa, might end-up as a satellite of Neptune. The weak gravity has a major advantage. Because also rocks inside the moon will weight little, massive mining operations can occur without risks. Huge caverns can be built. It will be possible to cross the entire moon with tunnels. Commerce Larissa will provide the colonies around Neptune with metals and minerals that otherwise should be shipped from the Inner Solar System. Because water ice still remains the main constituent and because of the huge distances, Larissa will never be able to export its minerals to the Inner Solar System, but it will be able to sell them around Neptune and maybe to the Kuiper Belt. There is a major challenge, however. It will be easy to ship goods to Proteus and other inner moons. Triton, the major moon of Neptune and the only one that is suitable for terraforming, is retrograde. Nereid has a highly elliptical orbit. The outer moons are far away. Shipping goods will be costly and will require much fuel to be spent. For cargo transports that don't require a limited time, the Delta-v calculator shows that it might be better to send them to an outer moon like Halimede (which will be the space station serving Neptune system) and from there to Triton or Nereid. Category:Moons